(a) Field of the invention:
The present invention relates to a straight guide driving device and, more specifically to a straight guide driving device suited for use to guide the vertical movement of the tube of a measuring microscope or the similar instrument.
(b) Description of the prior art:
The straight guide driving device used for vertical movement of the tube of a measuring microscope is generally disposed on an immovable member such as the body of a measuring microscope, and is equipped with a guide means for guiding a movable member such as the tube support, a driving shaft pivoted on the immovable member and having a pinion, and a rack fixed to the immovable member and engaged with the pinion. However, the pinion and rack are conventionally disposed on one side of the guide means, thereby posing a problem that accuracy of the vertical movement of the movable member is not maintained, i.e., measuring error is caused due to deviation of the center axis of the tube since turning moment is produced when the rack is driven by the rack and the direction of the turning moment is opposite between the ascending motion and descending motion. Further, when a measuring microscope is equipped with an optical rangefinder, the low accuracy of the vertical movement of the movable member is very serious since it is required to reserve a very narrow spacing between a scale attached to the immovable member and an index attached to the movable member.